1. Field of the Invention
The present invention relates to an apparatus and method for bend-shaping a glass sheet into a bi-directionally curved shape.
2. Description of the Prior Art
Many glass sheets for use as automobile side windows are bent in only one direction (hereinafter referred to as xe2x80x9csingle-curved glass sheetxe2x80x9d). Such glass sheets are known from, for example, Japanese Patent Publication No. SHO-43-11768 entitled xe2x80x9cMETHOD OF TRANSFERRING HEAT BETWEEN A GLASS SHEET AND GASES FLOWING IN CONTACT WITH THE SHEETxe2x80x9d (corresponding to U.S. Pat. No. 3,332,759 and U.S. Pat. No. 3,332,760).
For design reasons, such side window glass sheets are often required to be bent in two directions, namely, a first direction and a second direction normal to the first direction (hereinafter referred to as dual-curved glass sheet and often as xe2x80x9ccomplexly-curved glass sheetxe2x80x9d). An apparatus for bend-shaping such a complexly-curved glass sheet is proposed in, for example, Japanese Patent Laid-Open Publication No. HEI-5-009037 xe2x80x9cMETHOD AND APPARATUS FOR BEND-SHAPING A GLASS SHEETxe2x80x9d (corresponding to U.S. Pat. No. 6,014,873). An overall arrangement of the proposed apparatus is schematically illustrated in FIG. 15 hereof.
As shown in FIG. 15, the proposed apparatus includes a heating furnace 150 having an array of beds 151 (only one shown) positioned therein. Air is jetted from upper surfaces 151a of the beds 151 to floatingly support a glass sheet 153 for successively transferring, via a transfer means not shown, the glass sheet 153 over the upper surfaces 151a of the beds 151 in an arrowed direction.
Toward an outlet 150a of the heating furnace 150, the upper surfaces 151a of the beds 151 gradually become curved in a transverse direction (normal to a direction of transfer of the glass sheet 153) so that they have an upwardly convex shape. Thus, as the glass sheet 153 is transferred over the upper surfaces 151a in the arrowed direction, the glass sheet is gradually bent by its own weight (self-sagging) into a shape complementary with the shape of the beds 151 to thereby provide a single-curved glass sheet.
After arrival at a position proximate to the outlet 150a of the heating furnace 150, the single-curved glass sheet 153 advances inclinedly upwardly over beds 155, 156 disposed within the heating furnace (hereinafter called xe2x80x9cin-furnace bedsxe2x80x9d) in an upwardly inclined fashion. These beds 155, 156 have respective upper surfaces 155a, 156a curved not only in a transverse direction but also in the direction of transfer of the glass sheet. Thus, transfer of the single-curved glass sheet 153 over those beds 155, 156 causes the glass sheet 153 to become a complexly-curved glass sheet which is bent in both transverse and transfer directions of the glass sheet 153.
Continuously, the complexly-curved glass sheet 153 is transferred to a cooling bed 160 positioned proximately to and externally of the outlet 150a of the heating furnace 150 (hereinafter called xe2x80x9cout-furnace bedxe2x80x9d), where, while being supported by air jetted from an upper surface 160a of the out-furnace bed 160 in a floated fashion, the complexly-curved glass sheet 153 is cooled by cooling air jetted from cooling means 162 positioned upwardly of the glass sheet 153.
Reference is made next to FIG. 16 illustrating a conventional in-furnace bed on an enlarged scale.
Upper surface 156a of the in-furnace bed 156 is curved both in a direction of its width W and in a direction of its length L. The upper surface 156a of the in-furnace bed 156 has a multiplicity of air jet holes 157. Air is jetted from the air jet holes 157 to floatingly support the single-curved glass sheet 153 over the upper surface 156a, whereupon the glass sheet 153 is bent also in the direction of transfer of the glass sheet to thereby provide the desired dual-curved glass sheet.
Similarly to the upper surface 156a of the in-furnace bed 156, the upper surface 160a of the out-furnace bed 160 shown in FIG. 15 is curved both in a transverse direction and in a direction of transfer of the glass sheet.
Apart from the publication just described, an apparatus for bend-shaping a glass sheet into a dual-curved shape is also disclosed in Japanese Patent Laid-Open Publication No. HEI-6-191867 (U.S. Pat. No. 5,522,912). In the apparatus of this publication, a final bed disposed in heating furnace is curved in a transverse direction but is linear in a direction of transfer of a glass sheet. The final bed has an upper surface of uphill shape, that is, uprising toward an outlet of the heating furnace. In contrast, a quenching bed disposed externally of the heating furnace has an upper surface of downhill shape. Upon transfer from the final bed onto the quenching bed, the glass sheet is formed into a dual-curved glass sheet.
Another method and apparatus for bend-shaping a glass sheet is disclosed in Japanese Patent Laid-Open Publication No. HEI-9-202633. This publication teaches jetting hot air downwardly and combining a downward force produced by the jetted hot air with the weight of a glass sheet being bent to thereby facilitate bending of the glass sheet. As a result, the time required for bending a glass sheet can be shortened. Further, the hot air is jetted downwardly through a gap between an inclined bed and a cooling bed to provide an air curtain which keeps cooling air away from the glass sheet to thereby maintain the glass sheet at its softening temperature.
It is costly to install two lines of manufacture, namely, one for manufacturing the single-curved glass sheet, as described above, and the other for manufacturing the dual-curved glass sheet, as also described above. If a single line of manufacture is made available for use in producing both the single-curved glass sheet and dual-curved glass sheet, this will achieve substantial cost reduction.
For example, the in-furnace beds 155, 156 of the bend-shaping apparatus disclosed in Japanese Patent Laid-Open Publication No. HEI-5-009037, discussed with reference to FIG. 15, may be replaced with new beds 151, 151 curved only in a transverse direction, while the out-furnace bed 160 may be replaced with a bed curved only in a transverse direction. This makes the bend-shaping apparatus available for use in manufacturing a single-curved glass sheet.
Thus, only the bend-shaping apparatus as shown in FIG. 15 may be installed for manufacturing a single-curved glass sheet. When desired, relevant parts of the apparatus may be substituted by other parts to manufacture a dual-curved glass sheet. However, this involves tedious operations to switch the apparatus from one mode of operation to another by replacing the beds for manufacturing a single-curved glass sheet with the beds 155, 156 for manufacturing a dual-curved glass sheet.
Further, upon changing the beds for manufacturing the single-curved glass sheet to the beds 155, 156 for manufacturing the dual-curved glass sheet, it is necessary to lower the temperature of the heating furnace from about 700xc2x0 C., (glass softening temperature) to an atmospheric temperature. In addition, after the beds for manufacturing the single-curved glass sheet to the beds 155, 156 for manufacturing the dual-curved glass sheet, the temperature within the furnace 150 must be risen to about 700xc2x0 C. again. Consequently, bed changing takes a relatively long time, thereby deteriorating productivity. Moreover, it is necessary to provide two different types of beds, namely, beds 155, 156, 160 for manufacturing the dual-curved glass sheet and beds for bending the glass sheet, thereby increasing the cost of glass sheet production.
It is therefore an object of the present invention to provide an apparatus and a method for bend-shaping a glass sheet, which is capable of increasing productivity and reducing installation costs.
According to one aspect of the present invention, there is provided an apparatus for bend-shaping a glass sheet, which comprises: a heating furnace for heating the glass sheet, transferred therethrough along a path of travel thereof, to a substantially softening temperature of the glass sheet, the heating furnace having an inlet positioned upstream of the path of travel and an outlet positioned downstream of the path of travel; a plurality of in-furnace beds disposed within the heating furnace, each of the in-furnace beds having an upper surface of upwardly convex shape with a curvature increasing progressively toward the outlet of the heating furnace, the upper surfaces being designed to jet hot air against the glass sheet to support the glass sheet in a floated state thereover such that the glass sheet bends transversely by its own weight complementarily to the shape of the upper surfaces; at least one out-furnace bed disposed externally of the heating furnace proximately to the outlet of the heating furnace, the out-furnace bed having an upper surface of upwardly convex shape, the in-furnace beds and the out-furnace bed being arranged linearly along the path of travel; and an elevating mechanism, disposed below a downstream end of that one of the in-furnace beds which is positioned proximately to the outlet of the heating furnace and below an upstream end of the out-furnace bed, for elevating the downstream end of the one in-furnace bed and the upstream end of the out-furnace bed to cause the one in-furnace bed and the out-furnace bed to form a hill sloped in a direction along the path of travel, so that upon passage over the hill, the glass sheet bends longitudinally by its own weight complementarily to the shape of the hill, the upper surface of the out-furnace bed being designed to jet cold air against the glass sheet transferred past the outlet of the heating furnace to cool down the glass sheet while supporting the same in a floated state thereover.
By operating the elevating mechanism, the degree of inclination of the uphill formed by the one in-furnace bed and of the downhill formed by the out-furnace bed can be adjusted. Consequently, the dual-curved glass sheet can be readily produced by a simple operation to arrange the one in-furnace bed and the out-furnace bed to form the hill. With the one in-furnace bed and out-furnace bed returned to their original flat positions by operating the elevating mechanism, the bend-shaping apparatus can also be used for bend-shaping a single-curved glass sheet. Stated otherwise, the bend-shaping apparatus as arranged above enables production of both the single-curved glass sheet and dual-curved glass sheet without requiring changing of the beds but by simply causing the one in-furnace bed and the out-furnace bed to be inclined in such a manner as to form the hill. In addition, the beds for producing the single-curved glass sheet can also be used for producing the dual-curved glass sheet. This leads to the advantage that switching from one mode for the production of the single-curved glass sheet to another mode for the production of the dual-curved glass sheet becomes unnecessary.
Desirably, the bend-shaping apparatus further comprises a slide mechanism for sliding at least one of the one in-furnace bed and the out-furnace bed in the direction along the path of travel of the glass sheet. Provision of the slide mechanism makes it possible to move the one in-furnace bed and the out-furnace bed toward one another so that a gap defined between the downstream end of the one in-furnace bed and the upstream end of the out-furnace bed when these beds are arranged to form the hill can be kept to a minimum. This leads to the advantage that the glass sheet can be transferred smoothly from the one in-furnace bed to the out-furnace bed.
Preferably, the one in-furnace bed has a downstream end surface of curved configuration, while the out-furnace bed has an upstream end surface of curved configuration. This enables the downstream end surface of the one in-furnace bed and the upstream end surface of the out-furnace bed to come closer to each other when those beds are arranged to form the hill, thereby further narrowing the gap between the downstream end surface of the one in-furnace bed and the upstream end surface of the out-furnace bed.
Alternatively, the downstream end surface of the one in-furnace bed may have a lower corner while the upstream end surface of the out-furnace bed may have a lower corner, at least one of which lower corners is chamfered. This also enables the downstream end surface of the one in-furnace bed and the upstream end surface of the out-furnace bed to come closer to each other so that the gap defined between those end surfaces when the one in-furnace bed and the out-furnace bed are arranged to form the hill can be kept to a minimum.
In a preferred form, the bend-shaping apparatus further includes a guide roll, disposed in the space defined between the one in-furnace bed and the out-furnace bed, for guiding the glass sheet along the path of travel. This makes it possible to smoothly transfer the glass sheet pulled past the outlet of the heating furnace onto the out-furnace bed.
The guide roll may have a curved configuration conforming to the curved shape of the glass sheet so that the glass sheet can be supported in its entire transverse area by the roll, thereby facilitating smooth transfer of the glass sheet onto the out-furnace.
The bend-shaping apparatus may further includes an air jet nozzle, disposed in the space defined between the one in-furnace bed and the out-furnace bed, for jetting air against the glass sheet to thereby guide the latter along the path of travel. The air jetted from the air jet nozzle makes up for that part of a force for floating the glass sheet that may be lost by arranging the one in-furnace bed and the out-furnace bed in the hill form (inverted V-shape).
According to another aspect of the present invention, there is provided a method for bend-shaping a glass sheet in a bend-shaping apparatus including a heating furnace having an outlet positioned downstream of a path of transfer of the glass sheet, a plurality of in-furnace beds disposed within the heating furnace, at least one out-furnace bed disposed externally of the heating furnace proximately to the outlet in end to end relation to that one of the in-furnace beds which is positioned proximately to the outlet, the in-furnace beds and the out-furnace bed having upper surfaces curved transversely, the method comprising the steps of: elevating a downstream end of the one in-furnace bed and an upstream end of the out-furnace bed to a predetermined bed inclination height H so that the one in-furnace bed and the out-furnace bed jointly form a hill which allows to impart a desired radius of curvature C to the glass sheet, the bed inclination height H being obtained by first determining a first relation between the bed inclination height H and an apparent bed radius of curvature R on a basis of a length L1 of the one in-furnace bed forming an uphill of the hill, a length L2 of the out-furnace bed forming a downhill of the hill, the bed inclination height H, and a length G of the glass sheet in a direction of transfer thereof, and then determining a second relation between the apparent bed radius of curvature R and the radius of curvature C of the glass sheet; heating the glass sheet in the heating furnace to a substantially softening temperature of the glass sheet and jetting hot air from the upper surfaces of the in-furnace beds to floatingly support the glass sheet in such a manner as to allow the glass sheet to bend by own weight thereof transversely complementarily to the shape of the transversely curved in-furnace beds; transferring the transversely bent glass sheet over the hill so that the glass sheet bends longitudinally complementarily to the shape of the hill sloped in the direction of transfer; and transferring the bi-directionally bent glass sheet past the outlet onto the out-furnace bed and jetting cold air from the upper surface of the out-furnace bed to cool the bi-directionally bent glass sheet while floatingly supporting the latter.
By virtue of the hill sloped in the direction of transfer, the glass sheet can be bent in the direction of its transfer upon transfer of the glass sheet over the hill. Further, since the interrelations between the bed inclination height H, apparent bed radius of curvature R, and glass sheet radius of curvature C are pre-determined, the bed inclination height H can be readily obtained from such interrelations. If it were not for such interrelations, the operation to bend the glass sheet in the direction of its transfer becomes tedious and time consuming because repeated adjustments of the bed inclination height H become inevitable and the glass sheet must be checked to see if it has a desired radius of curvature after each adjustment.
Desirably, curvature (1/C) represented as a reciprocal of the glass sheet radius of curvature C falls in a range of 0 less than (1/C) less than 1xc3x9710xe2x88x924 mmxe2x88x921. 0 less than (1/C) is used herein because the glass sheet radius of curvature C becomes infinite when (1/C)=0, resulting in the production of a single-curved glass sheet linear in the direction of its transfer. Thus, 0 less than (1/C) is required for the production of a dual-curved glass sheet. The reason for the adoption of (1/C) less than 1xc3x9710xe2x88x924 mmxe2x88x921 is that if (1/C)xe2x89xa71xc3x9710xe2x88x924 mmxe2x88x921 is used in its stead, the glass sheet radius of curvature C becomes smaller than 1xc3x97104 mm. This makes the bed inclination too excessive and smooth transfer of the glass sheet difficult to achieve. There is also a fear that the lower surface of the glass sheet may be scratched by interfering with the beds laid in an angled fashion. Further, it may also become difficult to smoothly bend the glass sheet in the direction of its transfer. Thus, the vertical movement of the beds is restricted to (1/C) less than 1xc3x9710xe2x88x924 mmxe2x88x921. As a result, the glass sheet can be prevented from being damaged at a lower surface thereof during its transfer over the hill.
In a preferred form, the relation between the apparent bed radius of curvature R and the glass sheet radius of curvature C is represented by the expression: R=0.43xc3x97C+12.8xc3x97103 (unit: mm). From this expression, the apparent bed radius of curvature can be readily obtained.
The cooling of the glass sheet over the out-furnace bed may comprise air quenching the glass sheet.